Butanol Tolerance Regulated By A Two-component Response Regulator Slr1037 In Photosynthetic Synechocystis Sp. PCC 6803

Butanol is a promising biofuel with better chemical properties, and recent metabolic engineering efforts have demonstrated the use of photosynthetic cyanobacterial hosts as “microbial factories” for its production. However, butanol is always toxic to cell and cyanobacteria have very low tolerance to biofuels, limiting the economic viability of biofuels production from these renewable producing systems.In previous studies, we have found that a few two-component signal transduction systems(TCSTSs) were differentially regulated in Synechocystis sp. PCC 6803 after butanol treatment. To explore regulatory mechanisms of butanol tolerance, in this work, by constructing gene knockout mutants of the butanol-responsive TCSTS genes and conducting tolerance analysis, we uncovered that an orphan slr1037 gene encoding a novel response regulator was involved in butanol tolerance in Synechocystis. Interestingly, the ?slr1037 mutant grew similarly to the wild type under several other stress conditions tested, which suggests that its regulation on butanol tolerance is specific. Using a quantitative iTRAQ LC-MS/MS proteomics approach coupled with real-time reverse transcription PCR, we further determined the possible butanol-tolerance regulon regulated by Slr1037. The results showed that, upon slr1037 deletion, proteins involved in photosynthesis and glycolysis/ gluconeogenesis of central metabolic processes, and glutaredoxin, peptide methionine sulfoxide reductase and glucosylglycerol-phosphate synthase with stress-responsive functions were down-regulated, suggesting that Slr1037 may exhibit regulation to a wide range of cellular functions in combating butanol stress. Through slr1037 overexpression and phenotype analysis, we further confermed that slr1037 was involved in butanol tolerance because the overexpress-strain grow significantly better than that of wild type under the same butanol stress.This study revealed the first signal transduction protein identified directly related to butanol tolerance, the response regulator Slr1037, and it could be a natural candidate for transcriptional engineering to improve butanol tolerance in Synechocystis.